Serpentine3D

An open-source NURBS surface modeller for Linux, with native AI integration via MCP.

Serpentine3D (serp3d) is a freeform surface modeller in the spirit of Rhinoceros 3D — BREP/NURBS geometry on the OpenCASCADE kernel, not meshes. It is built for set designers, architects, and industrial designers who want a genuine Rhino-style workflow on Linux: a command line that prompts for input, layers, object snaps to a construction plane, STEP/OBJ interchange, and a dark, focused interface.

Named for the serpentine stone of Zimbabwean Shona sculpture, and for the S-curve at the heart of NURBS geometry.

Why

• No genuine open-source NURBS modeller exists for Linux. FreeCAD is parametric CAD; Blender is mesh-based. Serpentine3D fills the freeform surface-modelling gap.
• First CAD tool with native AI integration. The bundled MCP server lets Claude (or any MCP client) see your viewport, create geometry, run any command, and manage the scene.

Install

Requires Python 3.10+ on Linux with OpenGL 3.3.

git clone <this-repo> && cd Serpentine3D
python3 -m venv .venv
.venv/bin/pip install -e .
.venv/bin/serp3d        # launch

The OpenCASCADE kernel ships as pip wheels (cadquery-ocp) — no conda, no system packages.

The command line

Everything works Rhino-style: type a command, answer its prompts. Prompts accept typed coordinates (10,5,0, relative @5,0,0) or viewport clicks on the construction plane. Tab completes command names, Up/Down recall history, Enter on an empty line repeats the last command, Escape cancels.

	Commands
Curves	line polyline curve (interpolated NURBS) circle arc ellipse rectangle helix textobject blendcrv project pull intersect
Surfaces	extrude revolve loft sweep1 sweep2 planarsrf patch/networksrf offsetsrf unrollsrf
Solids	box sphere cylinder cone torus filletedge chamferedge (both pick edges directly; fillets chain and take start,end variable radii) shell cap contour booleansplit pushpull
Deform	twist taper bend flow (curve-to-curve) extend matchcrv
Booleans	booleanunion booleandifference booleanintersection
Transform	move copy rotate scale scalenu mirror array
Edit	join explode trim split offset fillet rebuild pointson/pointsoff (control points, curves and surfaces) delete hide show rename undo redo
Select	selall selnone selcrv selsrf selsolid sellayer selname sellast invert isolate unisolate
Organise	group/ungroup lock/unlockall block insert blocklist count
Camera	camera (lens mm, cinema sensors, placement, 2.39/1.85 frame guides) units cplane
Array	array (grid) arraypolar arraypath (along a curve)
Analysis	distance length area volume curvature zebra curvaturegraph (combs) draftanalysis
View	top front right perspective 4view/1view zoomextents wireframe shaded ghosted rendered technical grid snap
Render	material (Matte/Plastic/Metal/Glass/custom PBR — flows into GLB/USD export) rendered
Layers	layer (new/current/show/hide/rename/weight) — or use the Layers panel
Meshes	heavy OBJ/3DM props stay native meshes (instant display); meshtobrep / breptomesh convert
Files	new open save import export (.serp is a zip container with thumbnail + metadata)
Live	recordhistory — loft/extrude/revolve outputs rebuild when their input curves are edited

Most commands have Rhino-compatible aliases (l, pl, c, m, co, mi, ...). Command options appear as clickable chips under the prompt (Cap=Yes, BothSides=No, Style=Normal) and can be typed Rhino-style (cap=n) at any moment without losing your place; numeric prompts show a live gold ghost preview of the result while you type. help (or F1) opens a searchable command reference. Arrow keys nudge the selection along the CPlane (Shift ×10, Ctrl ×0.1).

Navigation & shortcuts

• Middle mouse orbit · Shift+Middle pan · Scroll zoom
• F1–F4 top/front/right/perspective · Ctrl+E zoom extents · F7 grid
• Ctrl+Z / Ctrl+Y undo/redo · Ctrl+A select all · Delete delete selection
• Ctrl+S / Ctrl+O / Ctrl+N save/open/new
• Click to select (Shift-click adds, Ctrl-click removes), click empty space to deselect
• Box selection: drag left-to-right for a window (fully enclosed, gold box), right-to-left for a crossing (anything touched, white box); Shift adds, Ctrl removes
• Control points: pointson (F10) shows CVs on curves — drag a CV to edit the curve live; pointsoff (F11) hides them
• Object snaps — end, mid, center, quadrant, intersection, perpendicular, and nearest-point, each with a distinct cursor marker. Toggle types on the osnap bar under the command line, or in Settings. gridsnap snaps picked points to the grid
• Launch with a file: serp3d model.serp (or any importable format)

Drafting & documentation

Serpentine3D has a full two-space drafting workflow — model in 3D, document in 2D, print to PDF — without leaving the app:

• Layouts (layout): paper-space sheets (A4–A0, Letter, Tabloid or custom) with tabs at the bottom of the viewport: [Model] [Sheet 1] …
• Detail views (detail): live windows into the model placed on the sheet — pick two corners, a view direction (top/front/right/…/perspective) and a scale (1:10, 1:50, …). Double-click a detail to enter it, then pan (nav-button drag) and zoom (wheel changes the scale); click outside to exit. detailscale, detailmode, detaillock, detailborder, detaildelete manage the active detail.
• Hidden-line rendering: each detail can be technical (hidden lines removed), hidden (dashed hidden lines), wireframe or shaded — powered by OCCT's HLR engine, isolated in a worker process so degenerate geometry can never crash the app. The same engine drives the model-space technical display mode.
• make2d: project the current view (or a selection) into real, editable 2D curves on Make2D visible / Make2D hidden layers.
• Annotations: multiline text, leader, dim / dimradius / dimdiameter / dimangle, hatch (pick corners or Mode=Region to click inside detail linework), scalebar, titleblock, sheetindex and per-sheet revision tables. Everything on a sheet is selectable — drag to move, grips resize detail frames, Delete removes, annotedit edits — and dimensions picked inside a detail are associative: they re-project when the detail pans or rescales. dimstyle manages named text/arrow styles.
• exportpdf (Ctrl+P): true vector PDF — linework stays crisp at any zoom; shaded details are embedded as rendered images. Layouts save/load with the .serp file.

The gumball

Select anything and a gumball appears: drag the arrows to move along an axis, the pads to move in a plane, the circles to rotate (Shift snaps to 15°), the square knobs to scale along an axis (Shift = uniform). Alt-drag moves a copy. Escape cancels a drag. gumball toggles it.

Units

units sets the document units (mm/cm/m/in/feet-and-inches) with an optional model rescale. Every prompt then accepts unit input — 3'6", 2' 4 1/2", 30cm, 1.5in — and coordinates support polar entry (10<45) and Shift-ortho constraint while picking.

Scripting & automation

• Python console (Tools menu, Ctrl+`): the live scene, geometry builders and the full API in an interactive session.
• serpentine3d.scripting.Document: the same power headless — doc.add(geo.make_box(...)), doc.run("filletedge", [...]), doc.export("part.step").
• serp3d-batch script.py: run scripts from the command line / CI with doc, geo and args predefined. No display needed.
• Autosave & crash recovery: every 5 minutes (configurable); on launch after a crash Serpentine3D offers to restore the autosave.
• Drop a ~/.config/serpentine3d/template.serp to start every new document from your own template (units, layers, title blocks).

Settings

Tools → Settings (Ctrl+,) — five flat pages, changes apply instantly:

• Mouse — orbit with the middle or right mouse button, scroll direction, orbit/zoom speed
• Keyboard — bind any key to any command; import from a text file (F5 zoomextents per line) or JSON
• Aliases — custom command aliases; imports Rhino alias exports (Options → Aliases → Export) and maps known commands automatically
• Object Snaps and Display (grid size)

Settings live in ~/.config/serpentine3d/settings.json.

File formats

Format	Import	Export	Notes
.serp	✓	✓	Native: JSON scene + embedded binary BREP
.step / .stp	✓	✓	Exact BREP exchange via OCCT
.3dm	✓	✓	Rhino: exact NURBS curves both ways; breps/surfaces import as untrimmed NURBS faces, export as meshes; layers preserved
.obj	✓	✓	Tessellated mesh with .mtl colours
.dxf	✓	✓	Curves/meshes with layers; layout sheets export at paper scale
.svg	✓	✓	Paths import as curves (béziers exact); layouts export as vector SVG
.glb		✓	Binary glTF with materials (Unreal/Blender/web)
.usda		✓	USD for virtual-production pipelines

MCP server (AI integration)

Serpentine3D exposes its full modelling surface as MCP tools. Start the app, then register the server with your MCP client:

claude mcp add serpentine3d -- /path/to/.venv/bin/serp3d-mcp

Tools: serp_scene_info, serp_screenshot (returns an image of the viewport), serp_create_curve, serp_create_surface, serp_boolean, serp_transform, serp_select, serp_command (run any command with its interactive inputs), serp_layers, serp_import, serp_export, serp_measure, serp_undo, serp_viewport.

The combination of serp_screenshot and serp_command means an AI assistant can model alongside you: it sees what you see and can operate every tool the command line offers. The bridge is a localhost-only JSON-RPC socket (~/.serpentine3d/rpc.port); set SERP3D_NO_RPC=1 to disable it.

Architecture

serpentine3d/
├── core/          # kernel layer: geometry builders, tessellation,
│                  #   scene graph, layers, selection, undo history
├── commands/      # generator-based interactive commands (Rhino-style
│                  #   prompt protocol, shared by GUI + MCP)
├── ui/            # Qt: GL viewport, command line, panels, dark theme
├── fileio/        # .serp / STEP / OBJ
├── mcp_server/    # stdio MCP server -> RPC bridge
├── api.py         # programmatic API over a running session
└── rpc.py         # localhost JSON-RPC bridge

Geometry is exact BREP on OpenCASCADE 7.9 (via the OCP pybind11 bindings); the viewport tessellates on demand with trim-aware isocurve display. Commands are Python generators that yield typed input requests — the same command code serves typed input, viewport clicks, and MCP calls.

Plugins

Drop a .py file into ~/.serpentine3d/plugins/ defining serpentine3d_plugin(ctx), or ship a package with a serpentine3d.plugins entry point — plugins register first-class commands (with prompts, osnaps, undo and MCP support for free) and menu items. See docs/scripting.md.

Development

.venv/bin/pip install -e ".[dev]"
.venv/bin/pytest            # unit tests (geometry, scene, commands, file I/O)

License

MIT